1. Field of the Invention
This invention relates to a scanner (inclusive of a color copier, a color facsimile machine, etc.) having a two-line sensor, which comprises a line sensor (a linear image sensor) for the color green in which a plurality of photodiodes (photo elements) corresponding to pixels are arranged in a row and filters which allow transmission of a green light component are provided on the light-receiving surfaces of the photo elements so that the sensor will output a green image signal representing an image of interest, and a line sensor for both the colors red and blue in which a plurality of photo elements corresponding to pixels are arranged in a row and in parallel with the line sensor for the color green and filters which allow transmission of a red light component and filters which allows transmission of a blue light component are alternately provided on the light-receiving surfaces of the photo elements so that the sensor will output a red image signal and a blue image signal representing the image of interest, and conveyance means for conveying the image of interest (and the two-line sensor relative to each other. The invention relates further to a method of generating interpolated pixels in this scanner.
2. Description of the Related Art
In a scanner of the kind described above, the number of pixels of the image of interest represented by the green image signal and the number of pixels of the image of interest represented by the blue or red image signal do not agree because the line sensor for the colors red and blue has the filters which allow the transmission of the red light component and the filters which allow the transmission of the blue light component provided on the light-receiving surfaces of the photo elements in alternating fashion. For this reason pixels are interpolated with regard to the image of interest represented by the blue image signal or red image signal so that the number of pixels will be made to coincide with the number of pixels of the image of interest represented by the green image signal. As a consequence of such pixel interpolation, the edge portion of the image of interest develops false colors when the image of interest read using a scanner is displayed.
In order to prevent the occurrence of false colors, an optical low-pass filter is inserted into image sensing optical system to eliminate the high-frequency components that are the cause of false color generation.
In the two-line sensor described above, the sampling frequency of the green image signal output by the line sensor for the color green and the sampling frequency of the red image signal and blue image signal output by the line sensor for the colors red and blue are different. Consequently, when the cut-off frequency of the optical low-pass filter is made to conform to the sampling frequency of the green color signal output by the line sensor for the color green, there are instances where the image of interest represented by the red image signal and the image of interest represented by the blue image signal develop false signals as before. When the cut-off frequency of the optical low-pass filter is made to conform to the sampling frequencies of the red image signal and blue image signal output by the line sensor for the colors red and blue, the resolution of the displayed image of interest declines.